This invention relates to a method of making a continuous envelope structure and, more particularly, to one wherein the envelope structure is particularly adapted to be processed through a computer printer.
Increasingly, envelopes are addressed in computer printers programed to utilize lists of selected recipients. Thus, an extensive mailing can be achieved with a minimum of manual labor. Machines and devices are available for stuffing, sealing, etc. the addressed envelopes. A problem has existed in providing the envelopes in a connected series (usually zig-zag folded) whereby they can be stepped through the computer printer at high speed, yet achieve reliable and accurate results. None of the solutions proposed in the art so far fully meet the requirements of reliable operation on the computer or in the insertor or ultimate neat appearance.
These problems have been solved according to the instant invention by utilizing what might be called a "shingling" procedure, i.e., wherein the envelope front plies are discrete and overlapped, one on another, relative to a continuous ply which provides the envelope backs. To this extent, it is somewhat reminiscent of the prior art of U.S. Pat. No. 2,790,593. However, that patent required precision in placing of the front plies in order to obtain a zig-zag foldability and the mandatory neat appearance. Such precision was, and is, practically impossible. For example, if the top ply overlaps the fold line at all, a satisfactory pack cannot be folded -- and if the top ply falls short, it exposes the bottom ply and gives a poor appearance.
Therefore, the art has not utilized the "continuous back ply" approach but instead has gone to either continuous front plies or utilized an approach where both plies are continuous. A continuous front ply with a "patch-on" back presents feeding problems on many present day computers. When bot plies are continuous, the openings in the pack present the same feeding problems and also result in large wastage in the back ply, typically 25%.
According to the invention, front plies are assembled on a continuous back ply in overlapped or shingled relation. Thereafter, the front and back plies are simultaneously weakened along transverse lines to develop the lines for zig-zag folding, the means for separating the individual envelopes from the continuous stream and also, if preferred, the line for folding the flap of the envelope into closed position. The stress used to separate the envelopes is not applied however, to the flap fold perforation. Also in the preferred embodiment, control margins are provided in the structure so as to facilitate stepping or indexing of the continuous envelope structure through the computer printer. Other advantages and details of the invention may be seen in the ensuing specification.